1. Field of the Invention
This invention pertains to retort methods for heat treating containers, and more particularly relates to a method for evenly and efficiently heating or cooling all containers in a batch of containers while using a minimum of heat treatment liquid.
2. Description of the Prior Art
In general, prior art retort methods receive batches of containers, such as filled cans, jars, pouches or trays, which are first heated in hot water until sterilized and are thereafter cooled by cold water. In order to prevent damage to the containers when the pressure within the containers tends to exceed the pressure externally of the containers, an overriding air pressure is usually applied over the water in these prior art devices. The water in the pressure vessel or retort is usually caused to either cascade down upon the flat upper ends of the containers, or alternately is moved horizontally against the rounded surfaces of the upstream containers with little regard to whether or not the other containers in the batch of containers being processed, and especially those near the middle of the batch, receive the same amount of heat as the upper or outer containers.
The problem of providing uniform heat to each container has been solved by the method disclosed in the above mentioned Mencacci et al application (now U.S. Pat. No. 4,003,302) of which I am a co-inventor and which application is assigned to the assignee of the present invention. In the Mencacci et al device, containers are loaded into a tunnel within a closed retort and water is then circulated from one end to the other of the retort, which other end opens directly into the retort. In order to assure that the uppermost containers in the tunnel are completely immersed in flowing water, the water in the Mencacci et al retort, both within and externally of the tunnel, is maintained at a level above the tunnel. Thus, when changing from the cooking to the cooling cycle of operation, a very large amount of hot water externally of the tunnel must either be stored in a very large and expensive storage tank, or must be drained and thereafter cold water must be reheated for the next batch of containers with a substantial loss in heating energy.
U.S. Pat. No. 3,776,257 which issued to Piegza on Dec. 4, 1973 discloses a high pressure retort system with flat walls which separate an article and liquid filled heat treatment chamber from the outer curved area of the retort thereby reducing the amount of liquid processing medium required. A gas pressure is applied to the external surfaces of the flat walls to prevent pressure induced bowing of the flat walls.
The United States Greenberg et al U.S. Pat. No. 3,531,300 which issued on Sept. 29, 1970; and similar Katz et al U.S. Pat. No. 3,769,028 which issued on Oct. 30, 1973 both disclose a vertically oriented pressure vessel which uses a propeller for imparting a circulating movement to a heat transfer medium such as water, steam, or hot air. The containers being processed are illustrated as being pouches that are mounted in trays. However, neither of these patents disclose the use of a tunnel within which the batch of containers are evenly heat treated by virtue of a liquid moving into an inlet end of the tunnel and out the other end for return to the inlet and externally of the tunnel.